This proposal is designed to identify and characterize both intra-and extrahypothalamic pathways containing oxytocin and its associated neurophysin by bioassay, radioimmunoassay and immunocytochemistry. Subdivisions of the oxytocin system will be determined by application of these techniques after lesions of the paraventricular nucleus, and by retrograde tracing methods using horseradish peroxidase and orthograde methods with radiolabeled tracers. The stimulatory effects of estradiol on the oxytocin projections to the portal capillary system and posterior pituitary gland and a new oxytocin system with cell bodies in the temporal lobe sensitive to the steroid will be delineated. The inter-relationships of the catecholamine-containing system with oxytocin pathways will be studied by histofluorescence and the effect of their destruction by the administration of 6 OH-dopamine. The importance of the oxytocin part of this paraventricular nucleus in the milk ejection reflex and the influences of beta-endorphin, and catecholamine will be assessed in suckling rats with lesions in this nucleus. In order to assess specific rat oxytocin neurophysin, this neurophysin will be purified from homozygous Brattleboro rats which will permit specific radioimmunoassay, and specific immunocytochemistry of the light and electronmicroscopic level. This will also facilitate studies of probable oxytocin-containing synapses in brain and spinal cord.